War of the Colossal Beast picks up a year after the first movie ended -- Joyce Manning (Sally Fraser), sister to the first film's 70-foot-tall Colossal Man, Lt. Col. Glenn Manning (Glenn Langan), believes that her brother is still alive, despite his fall off of Boulder Dam at the denouement of the first movie. Her hope is based on reports out of Mexico about a "very big man" attacking truckers and other passersby in a remote part of the country. As it turns out, Manning (played here by Dean Parkin, since Langan turned down the request to star in a sequel) is alive and hiding somewhere in the mountains, bigger than ever and suffering from serious brain damage, with a hideously deformed face that is covered in scar tissue and missing an eye. Every effort at communicating with the giant fails, and as things always transpire in movies of this sort (at least since the silent version of The Lost World), he breaks out of the place where he is being held and goes on a rampage.
~ Bruce Eder, All Movie Guide